The coupling and lifting system provided by the invention is of the type that includes two lower longitudinal arms articulated in such a manner as to be capable of rising or descending and provided on their front ends with hitching means comprising two bottom hitching points, and one upper arm in the middle, also articulated, for hitching the implement at a third point. Means for controlling the rise and descent of the two lower arms and of the upper arm are provided, and the rear portion of the implement is provided with hitching means corresponding to the three points of the tractor. A rigid intermediate support frame is also provided for connection between the implement and the arm and includes two lateral bottom points and one middle top point for hitching the implement, as well as two lateral top points equidistant from the middle top point that are intended to be connected to the third top hitching point of the tractor by connecting means of variable length.
French Patent 2 562 752 describes a coupling and lifting system of this type that allows the implement to follow transverse contours by rotation about a longitudinal axis that is parallel to the direction of forward travel of the tractor and is centered on the coupling system. Furthermore, mounting the upper portion with two telescoping connections makes it possible, when the implement is in use and is resting on its gauge wheel or wheels, to obtain a rotation of the implement about a lower bar connected to two lateral lower coupling hooks, which also enables the implement to follow longitudinal contours.
The existence of two upper telescoping bars, which lock in an elongation position by the influence of the weight of the implement in the raised position, when the gauge wheels are clear of the ground, makes it possible to assure the stability of the implement while it is being raised and to avoid an untimely rotation that could make the implement dig into the ground while it is being raised.
Replacing the upper telescoping bars with hydraulic jacks, the function of which is controlled by load pickups associated with the gauge wheels, makes it possible to assure a transfer of weight to the tractor while continuing to follow the longitudinal and transverse contours perfectly.
This kind of coupling and lifting system functions perfectly, but its cost limits its development. Furthermore the presence of a longitudinal bearing in the lower middle portion of the support frame virtually prevents the usage of a power take-off to drive certain implements, since there is no possible passageway for a transmission shaft.